Neutralizing system



INPUT 3nvenltor James W Conlln 7 7 /WV m (Ittorney NEUTRALIZING 'SYSTEM Filed March 31, 1939 J. W. CONKLIN Aug. 13, 1940.

Patented Aug. 13, 1940 PATENTS OFFICE NEUTRALIZING SYSTEM James W. -Conklim Audubon,.N. J., assignor to i Radio Corporation of America, a corporation of Delaware i Application March 31, 1939, Serial No. 265,235

` 4 Claims.

This invention relates to neutrali'zing systems. Its primary purpose is to provide an improved mechanical arrangement for neutralizing radio frequency amplifiers, and has a particular application to ultra high frequency amplifiers of the parallel conductor tank circuit type.`

The usevof neutralizing' capacitors to prevent oscillation in a single or push-pull amplifier is well known' to those skilled in the art. In attempting to carry out the application of neutralizing capacitors to ,ultra high frequency circuits, several considerations became of importance if a stable arrangement is to be obtained. It is necessary to provide means for adjusting the neutralizing capacitors while the transmitter is in operation for the sake of convenience and to obtain the best possible adjustment. At the same time, it is necessary to avoid an arrangement in which the adjusting medium interferes with or disturbs the normal radio frequency eld in the vicinity of the neutralizing capacitors. Since the field is usually at a maximum at the point of neutralization, the circuit is quite sensitive to changes, so that the capacity of the hand or adjusting tools frequently makes complete neutralization quite difiicult. i

Since neutralizing capacitors are connected to the anode circuit, one plate is at a high positive direct current potential as well as at a high radio frequency potential. Suitable precautions must, therefore, be made to prevent danger to the operator when the neutralizing adjustment is being made. At ultra high frequencies, it is known that the current through the neutralizing capacitors may be twenty or thirty amperes, so that it is advisable to eliminate sliding contacts which frequently are a source of trouble where high currents are involved, and to provide a system in which direct contacts are provided between all of the circuits.

In accordance with this invention, an arrangement is provided in which the movable plates of the neutralizing capacitors are adjustably mounted on the tank circuit inductor and provision is made for pivotally rotating the entire tank circuit through a small arc to provide the neces- Sary neutralizing adjustment,

' This invention will be better understcod from the following description when considered inconnection with the accompanying drawing which illustrates a preferred embodiment of this invention.

Referring to the figure of the drawing, a halfwave parallel conductor tank circuit I constitutes the plate impedance of a push-pull amplifier i amplifier compartment.

which includes'a pair of tubes 3 and 5. Since the electrical connectio-ns are conventional, it is not necessary to illustrate the entire amplifier circuit in detail. The fundamental frequency of the z' tank circuit conductor is adjustable by means of a sliding bar 1 which short ,circuits the two conductors 9 and ll toadjustftheir length to the de'- sired frequency. The lower extremity of the tank circuit I is mounted o-n and supported by a resilient spring l3, which, in turn, is supported by two stand-off insulators 11, |1.

The upper, or high potential, end of the tank circuit 'is supported by a pair of porcelain insulators |9 and 2| which are firmly connected by a terminal block 23. A threaded thumb screw 25 extends through a shielding enclosure 21 of the The thumb screw is provided with a pair' of shoulders 24, 26 whichl prevents its longltudinal movement through the shield 21, but allow it'v to freely rotate therein. The free end of the thumb screw is threaded into the terminal block 23.

A par of neutralizing condensers are provided at the high radio frequency potential end-of the tank circuit I. prise fix'ed plates 29, 3| which are fixedly mounted o on an insulator 31 which is supported by the compartment shield 28 and movable plates 33, 35 which are, respectively, mounted on and connected to the open ends of the tank circuit conductors 9 and t In order to provide a coarseladjustment for th neutralizing capacitors, the movable plates 33 and 35 are preferably attached to the tank circuit conductors by threaded rods 39, 4|, which are provided With lock nuts to insure a tight electrical connection. g

Suitable connecting leads are utilized to complete the electrical circuit to the respective grid and anode electrodes of the amplifier tubes. To allow unrestricted motion for the adjustment of the neutralizing capacitors, the anode leads are preferably flexible. Input and output connections are made at coupling coils 43, 45 which are coupled, respectively, to the grid tank coil 41 and the anode tank l.

From a consideraton of the drawing, it is ap- 'parent that the neutralizing operation may be effected without danger to the operator and with complete freedom from' disturbance by turning 50 the thumb screw 25. The entire tank circuit is moved through a small angle to increase cr decrease the spacing between the plates of the neutralizing capacitors. Sliding contacts have been eliminatd. This Vaccordingly increases the stav55 The neutralizing capacitors com- 25 bility of the arrangement, partcularly at ultra high frequencies. Complicated mechanical drive arrangements which have heretofore been connected to the movable plates of the neutralizing capacitors have been eliminated. Inasmuch as an insulating support is necessary to hold the tank circuit in position regardless of the arrangement which may be used to adjust the neutralizing capacitors, it is apparent that the proposed system does not increase the material required, but in fact elimnates certain parts which have heretofore been deemed necessary.

While I have illustrated my invention by means of a push-pull radio frequency amplifier, it is evdent that this idea may likewise be applied to a single stage neutralizing amplifier or to the verm'er adjustment of the frequency of radio frequency oscillators or the like.

I claim as my invention:

1. A neutralized radio frequency amplifier which includes a pair of neutralizing capacitors, an inductor, fiexible mounting means for supporting said inductor at a point of minimum voltage, one plate of each capacitor being mounted on and connected to said inductor, and adjusting means for varying the position of the free end of said inductor to thereby vary the capacity of said capacitors.

2. A neutralized radio frequency amplifier which includes a pair of neutralizing capacitors, a parallel conductor tank circuit inductor, fiexible mounting means for supporting said inductor at a point of minimum voltage, one plate of each capacitor being mounted on said inductor, and means for varying the position of the free end of said inductor to thereby vary the capacity of said capacitors.

3. A neutralized radio frequency amplifier which includes a pair of neutralizing capacitors, a parallel conductor tank circuit closed at one end and open at the other, resilient means for mounting said inductor at said closed end, adjustable means for positiom'ng the open end of said inductor, and a pair of neutralizing capacitors including fixed and movable plates, said movable plates being adjustably mounted on respective conductors of said inductor whereby the capacity of said neutralizing capacitors is varied by said adjustable means.

4. A neutralized radio frequency amplifier which includes a pair of neutralizing capacitors, a folded half-wave parallel conductor tank circuit closed at one end and open at the other, means for pivotally mounting said inductor at said closed end, adjustable means remote from the radio frequency field of said inductor for positioning the open end of said inductor, and a pair of neutralizing capacitors including fixed and movable plates, one of said movable plates being adjustably mounted on each of said conductors whereby the capacity of said neutralizing capacitors may be varied by said adjustable 30 means.

J AMES W. CONKLIN. 

